1. Field of the Invention
The present invention relates to an embedding resin for embedding electronic parts such as chip capacitors, chip inductors, chip resistances, etc., in the inside of a substrate and to a wiring substrate (i.e., wiring board) having embedded electronic parts in the inside of the substrate. Particularly, the invention is suitable for a multilayer wiring substrate having formed fine wiring layers having a width of not wider than 150 xcexcm on the embedding resin, a package for containing (receiving) a semiconductor element, etc.
2. Description of the Related Art
Recently a multichip module (MCM) mounting many semiconductor elements on a build-up wiring substrate has been investigated. In the case of mounting electronic parts such as chip capacitors, chip inductors, chip resistances, etc., it is general to surface-mounting the electronic parts on a wiring layer for mounting formed on the surface of a wiring substrate using a solder.
However, when electronic parts are surface-mounted on the surface of a build-up wiring substrate, definite mounting area for various electronic parts is required, whereby there is, as a matter of course, a limit for the miniaturization. Also, by treating a wiring in the case of carrying out surface-mounting, the occurrence of a parasitic inductance, which is undesirable for characteristics, is increased and there is a problem that the correspondence of electronic instruments to high frequency becomes difficult.
For solving these various problems, various methods of embedding electronic parts in the inside of a substrate have been investigated. For example, Japanese Patent Laid-Open No. 126978/1999 discloses a method of, after previously solder-mounting electronic parts to a wiring substrate having a transfer sheet made of a metal foil, transferring the electronic parts, but, there remains a problem in the position precision, etc., at mounting. Also, Japanese Patent Laid-Open No. 124352/2000 disclosed a multilayer wiring substrate obtained by build-upping an insulating layer on electronic parts embedded in the inside of a core substrate.
For embedding electronic parts disposed in a wiring substrate in the inside of the substrate, it is necessary to embed the gaps among the core substrate and the electronic parts with the resin and electrically connecting the electrodes of the electronic parts to the wirings formed on the insulating layer by electroless plating, etc. In this case, by an ordinary embedding resin, the adhesion with a plated layer, which becomes the wiring, cannot sufficiently be insured to cause a problem of generating blister of plated layers, etc., in a reliability test. For example, even when the resin has a peeling strength exceeding 588 N/m in an initial state, but since by the influences of heat and moisture of the using environment, the peeling strength is deteriorated to become lower than 588 N/m, which gives a problem. Particularly, when a fine wiring layer having a width of not wider than 150 xcexcm is formed On an embedding resin or when a wiring layer of passing a large electric current, such as a power source layer is formed, it become a remarkably severe problem.
For improving the adhesion of the embedding resin and the plated layer, a method of first embedding the electronic parts using the embedding resin, then after roughening the surface of the embedding resin with an oxidizing agent such as permanganic acid, chromic acid, etc., a wiring layer is formed by plating, and making build-up layer (forming multilayers) is considered. This is because by the anchoring effect of the unevenness of the roughened surface, the adhesive force with the plated wiring layer is increased. This is known as a method of improving the adhesion of the wiring layer of a build-up wiring substrate and the insulating layer. However, for an embedding resin, the manner of easily roughening is not utterly considered and by the above-described method, the remarkable improvement of the adhesion is hard to be expected.
An object of the invention is to provide an embedding resin, which increases the mounting density of a wiring substrate mounting thereon electronic parts and obtains a high reliability in a reliability test, such as a heat resistance, a water resistance, etc., and to provide a wiring substrate using the resin.
The embedding resin of the invention is an embedding resin for embedding electronic parts disposed in an opening (a throughhole) or a concave portion such as cavity, etc., formed in a substrate, wherein the peeling strength of a copper layer after a pressure cooker test (121xc2x0 C., 100% by mass (by weight) humidity, 2.1 atm and 168 hours) of the substrate having formed the copper plate on the cured product of the embedding resin is at least 588 N/m (0.6 kg/cm). The peeling strength after the pressure cooker test (121xc2x0 C., 100% by mass humidity, 2.1 atm, and 168 hours) is more preferably at least 700 N/m (0.71 kg/cm). Since even by testing under such conditions, the peeling strength still insures the values of at least 588 N/m (0.6 kg/cm), even when a fine wiring layer having a width of not larger than 150 xcexcm is formed on the embedding resin and even when a wiring layer passing a large electric current, such as a power source layer is formed thereon, a high adhesive reliability can be insured.
In addition, the above-described electronic parts include passive electronic parts such as a chip capacitor, a chip inductor, a chip resistance, a filer, etc.; active electronic parts such as a transistor, a semiconductor element, FET, low-noise amplifier (LNA) etc., and other electronic parts such as a SAW filter, a Lc filter, an antenna switch module, a coupler, a diplexer, etc.
Also, in the embedding resin of the invention, it is preferred that the peeling strength of a copper layer in a pressure cooker test (121xc2x0 C., 100% by mass humidity, 2.1 atm and 336 hours) of a substrate hating formed the copper layer on the cured product of the embedding resin is at least 600 N/m (0.61 kg/cm). Since even by testing under such a severe condition, the peeling strength still insures the values of at least 600 N/m (0.61 kg/cm), even when a wiring layer for a power source layer connected to electronic parts such as a capacitor having a power source supplying function is formed on the cured product of the embedding resin, a higher adhesive reliability can be insured.
The measurement method of the peeling strength is carried out according to JIS C 5012 (1993), and in this case, the width of the copper layer is 10 mm. The peeling strength of peeling the copper layer from the surface of the embedding resin to the direction of 90 degree (vertical direction) at a pulling speed of 50 mm/minute is measured.
In the embedding resin of the invention, for coloring the resin to a black-base while keeping the peeling strength of the copper layer after the pressure cooker test (121xc2x0 C., 100% by mass humidity, 2.1 atm and 168 hours) at least 588 N/m (0.6 kg/cm), it is better to add carbon black in an amount of not more than 0.5% by mass, and preferably not more than 0.3% by mass. This is because the embedding resin can be colored to a black-base without reducing the adhesive reliability of the wiring layer at a high temperature and a high humidity and the volume resistance, which is the index of the insulating property.
Also, in the embedding resin of the invention, for coloring the resin to a black-base while keeping the peeling strength of the copper layer after the pressure cooker test (121xc2x0 C., 100% by mass humidity, 2.1 atm and 336 hours) at least 600 N/m (0.61 kg/cm), it is better to add carbon black in an amount of not more than 0.4% by mass, preferably not more than 0.3% by mass, and particularly preferably not more than 0.2% by mass.
This is because by increasing the adhesion of the wiring layer at a high temperature and a high humidity, the occurrence of the causes of inferiorities such as blister in the production process of the wiring substrate is prevented, whereby the improvement of the yield and the improvement of the insulation reliability are obtained.
It is preferred that the embedding resin is colored to black for restraining the occurrence of irregular reflection at the light exposure for cutting a wiring pattern and for preventing the generation of color shading at curing the resin. However, when carbon black is compounding with the resin for coloring in black base in an amount of at least a definite amount, the heat resistance and the moisture resistance of the resin are lowered and the adhesive power with copper is lowered.
The embedding resin of the invention is comprised of a resin component and at least one kind of an inorganic filler. The inorganic filler is incorporated for controlling the thermal expansion coefficient and also by the effects as the skeleton of the three-dimensional structure after curing an epoxy resin and as the aggregate given by the inorganic filler, the form of the embedding resin after the roughening treatment is not crumbled more than usual.
There is no particular restriction on the inorganic filler used but crystalline silica, fused silica, alumina, silicon nitride, etc., are preferably used. Since such an inorganic filler can effectively lower the thermal expansion coefficient of the embedding resin, the occurrence of pealing of the resin by thermal stress is prevented and the reliability can be improved.
The particle size of the inorganic filler used is preferably not larger than 50 xcexcm because it is necessary that the embedding resin also easily flows into gaps between the electrodes of the electronic parts. When the particle size of the filler exceeds 5 xcexcm, the filler becomes liable to be clogged in the gaps between the electrodes of the electronic parts, and by inferior filling of the embedding resin, portions of extremely different in the thermal expansion coefficient locally generate. The lower limit of the particle size of the filler is preferably at least 0.1 xcexcm. When the particle size of the filler is finer than 0.1 xcexcm, the fluidity of the embedding resin becomes hard to be insured. Thus, the particle size of the filler is preferably at least 0.3 xcexcm, and more preferably at least 0.5 xcexcm. For attaining a low viscosity and a high filling of the embedding resin, it is preferred to widen the particle size distribution.
For increasing the fluidity and the filling of the embedding resin, the form of the inorganic filler is preferably an almost spherical form. In particular, a silica-base inorganic filler is preferred since the spherical filler can be easily obtained.
It is preferred that, if necessary, the surface of the inorganic filler is subjected to a surface treatment with a coupling agent. As the kind of the coupling agent, silane-base, titanate-base, aluminate-base, etc., are used.
For the embedding resin of the invention, on taking into consideration of the fluidity thereof, it is preferred to use at least one kind of a bisphenol epoxy resin or naphthalene type epoxy resin, which is a liquid epoxy resin, a phenolnovolac type epoxy resin, and a cresol novolac type epoxy resin as the indispensable resin component. When the fluidity of the embedding resin is inferior, inferior filling becomes liable to occur in the gaps between the electrodes of electronic parts, whereby the portions having extremely different thermal expansion coefficient are locally occurred. In the case of considering the heat resistance and the moisture resistance, a naphthalene type epoxy resin is particularly excellent.
The wiring substrate having embedded electronic parts using the embedding resin of the invention has an advantage that by the influences of heat and moisture in the using environment, the peeling strength of the wiring layer formed in the embedding resin is not deteriorated. Particularly, the wiring substrate is suitable in the case of forming a fine wiring layer having a width of not larger than 150 xcexcm on the embedding resin and the case of forming a wiring layer passing a large electric current, such as a power source layer. Particularly, by improving the adhesion to the embedding resin of a wiring layer, which becomes a power source layer, when a large electric current is passed from a capacitor for power source supplying, the occurrences of selling of the wiring layer and the deterioration of the peeling strength of the wiring layer can be effectively prevented. The term xe2x80x9celectronic parts are embeddedxe2x80x9d in the invention means that after disposing electronic parts in an opening (a throughhole (shown, for example, in FIG. 2)) or a concave portion such as cavity (shown, for example, in FIG. 10) formed in a substrate such as a core substrate or a build-up insulating layer, the embedding resin is filled in the gaps formed between the opening and the electronic parts. Particularly, in the case of using a thin core substrate having a thickness of not thicker than 400 xcexcm, it is preferred to dispose electronic parts in a cavity formed in a build-up layer. It is preferred that for the opening, a throughhole formed by punching a substrate or a cavity, etc., formed by a multilayer-forming technique is utilized.
As the substrate, which is used in the invention, a so-called core substrate such as FR-4, FR-5, BT, etc., is preferably used but a core substrate formed by sandwiching a copper foil having a thickness of about 35 xcexcm in thermoplastic resin sheets such as PTFE sheets, etc., and having formed an opening may be used. Also, a substrate formed by alternately laminating an insulating layer and a wiring layer on at least one surface of a core substrate to form a build-up layer and having formed an opening penetrating the core substrate and the build-up layer can be used. In this case, even a multilayer wiring substrate of a capacitor build-in type as shown in FIG. 11, the thickness of a so-called glass-epoxy composite material (insulating substrate) is thinned to about 400 xcexcm, which is a half of 800 xcexcm of an ordinary product, to make a low back substrate. As other example, a wiring substrate having electronic parts embedded in the inside of the core substrate (as shown, for example, in FIG. 1) and wiring substrate having electronic parts embedded in the inside of a build-up layer (as shown, for example, in FIG. 10) can be formed.
It is better that the thickness of a substrate of embedding therein electronic parts is as near as the thickness of the electronic parts to be embedded. In particular, it is preferred to establish the relation of the height of electronic parts and the thickness of the substrate such that the distance from the surface of the terminal electrode of the electronic parts to the wiring layer of the build-up layer laminated on the substrate becomes not longer than 100 xcexcm (preferably not longer than 50 xcexcm, and more preferably not longer than 30 xcexcm). This is because by reducing the distance of the electronic parts to the build-up layer laminated on the substrate as small as possible, the generation of unnecessary parasitic capacities (inductance, etc.) can be prevented.
A multilayer wiring substrate, wherein a build-up layer formed by alternately laminating an insulating layer and a wiring layer is formed at least one surface of a core substrate, and a substrate having formed an opening such that the opening penetrates at least one of the core substrate and the build-up layer is used, may be produced, for example, as follows (FIG. 11 to FIG. 25).